1. Field of the Invention
The present invention relates to a deinterlacer, and more particularly, to a progressive scan method using edge dependent interpolation.
2. Description of the Related Art
In general, deinterlacers convert video signals of an interlaced scanning format into those of a progressive scanning format.
The video signals of an interlaced scanning format are generally used in Korea, Japan, and the United States. The video signals of a progressive scanning format are used for high definition televisions (HDTV). The deinterlacers are intended to make these two scanning formats for video signals compatible with each other by converting video signals of the interlaced scanning format into those of the progressive scanning format.
One deinterlacing interpolation technique is edge dependent interpolation, which is related to spatial interpolation. Edge dependent interpolation is different from temporal interpolation that involves filling empty lines of the current field with interpolated data of the previous or further previous field data. That is, edge dependent interpolation is related to spatial interpolation that involves forming frame data by filling empty lines of the current field with interpolated data within the current field when progressive scanning using inter-field interpolation cannot be carried out because a difference between two fields is too large at moving portions of a displayed image.
FIG. 1 is a diagram illustrating edge dependent interpolation used in a general progressive scan method used in a display. Referring to FIG. 1, spatial interpolation used in a general progressive scan method used in a display is directed to determining 3×3 pixel windows with respect to respective center pixels that are to be interpolated, i.e., x (i, j), and computing interpolated pixel data, i.e., {tilde over (x)} (i, j), which is obtained by progressively interpolating respective center pixels that are to be interpolated and to be filled in empty lines of the current field. At this time, since diagonal directions are at angles of 45° to horizontal lines, directions of edges are determined in relation to gradients of at least 45°.
In a case of edge dependent interpolation of 3×3 pixel windows as shown in FIG. 1, the interpolated pixel data, i.e., {tilde over (x)} (i, j), is computed as follows:
                    {                                                            a                ≡                                                                                              x                      ⁡                                              [                                                                              i                            -                            1                                                    ,                                                      j                            -                            1                                                                          ]                                                              -                                          x                      ⁡                                              [                                                                              i                            +                            1                                                    ,                                                      j                            +                            1                                                                          ]                                                                                                                                                                                      b                ≡                                                                                              x                      ⁡                                              [                                                                              i                            -                            1                                                    ,                          j                                                ]                                                              -                                          x                      ⁡                                              [                                                                              i                            +                            1                                                    ,                          j                                                ]                                                                                                                                                                                      c                ≡                                                                                              x                      ⁡                                              [                                                                              i                            -                            1                                                    ,                                                      j                            +                            1                                                                          ]                                                              -                                          x                      ⁡                                              [                                                                              i                            +                            1                                                    ,                                                      j                            -                            1                                                                          ]                                                                                                                                                                      (        1        )                                                      x            ~                    ⁡                      (                          i              ,              j                        )                          =                  {                                                                                                                (                                                                        x                          ⁡                                                      (                                                                                          i                                -                                1                                                            ,                                                              j                                -                                1                                                                                      )                                                                          +                                                  x                          ⁡                                                      (                                                                                          i                                +                                1                                                            ,                                                              j                                +                                1                                                                                      )                                                                                              )                                        /                    2                                    ,                                                                                                  min                    ⁡                                          (                                              a                        ,                        b                        ,                        c                                            )                                                        =                  a                                                                                                                                                (                                                                        x                          ⁡                                                      (                                                                                          i                                -                                1                                                            ,                                                              j                                +                                1                                                                                      )                                                                          +                                                  x                          ⁡                                                      (                                                                                          i                                +                                1                                                            ,                                                              j                                -                                1                                                                                      )                                                                                              )                                        /                    2                                    ,                                                                                                  min                    ⁡                                          (                                              a                        ,                        b                        ,                        c                                            )                                                        =                  c                                                                                                                                                (                                                                        x                          ⁡                                                      (                                                                                          i                                -                                1                                                            ,                              j                                                        )                                                                          +                                                  x                          ⁡                                                      (                                                                                          i                                +                                1                                                            ,                              j                                                        )                                                                                              )                                        /                    2                                    ,                                                            else                                                                        (        2        )            
In Equation 1, a, b, and c denote absolute differences between directional luminance of neighboring pixels of the center pixel x (i, j) that is to be interpolated. Thus, edge dependent interpolation is performed considering a direction in which luminance correlation is highest as a direction of an edge. Since the highest luminance correlation means the smallest change in directional luminance, edge dependent interpolation is carried out in a direction where the absolute difference between directional luminances is the smallest.
According to conventional edge dependent interpolation, a good display result is obtained in association with most general images. However, in relation to complex patterns with a number of high-frequency components, i.e., in a texture region, display quality is degraded even when compared with a progressive scan method that uses simple linear intra-field interpolation. Such degradation of display quality is caused by high-frequency noise introduced due to non-directional edge interpolation. Also, according to a progressive scan method using conventional edge dependent interpolation, directions of edges are determined in regions of gradients of at least 45° to horizontal lines by interpolation using 3×3 pixel windows. Thus, only simple linear interpolation is performed in a region of a low gradient below 45° without taking into consideration directional interpolation, which results in zigzagged edges.